The present invention relates to a cantilevered motor bearing apparatus and particularly to such a bearing apparatus for a permanent magnet motor such as used in computer disk drives.
The development of computer memories using rotating disks has created a demand for small, high speed drives which accurately rotate and position disk memories. Motors using a permanent magnet rotor in combination with multiple pole stator have been used in such drives. The rotor shaft is mounted within the stator by a suitable bearing structure, with the rotor secured to the outer end of motor shaft and defining a cantilevered bearing support. The disk drive is secured to the opposite end of the motor shaft. The bearing structure must provide accurate and long-life support for the cantilevered mounted rotor. Various sleeve and ball bearing structures have been suggested for use in permanent magnet motors for disk drives. In one ball-bearing unit, a pair of axially spaced high precision rotary ball bearings are secured within a machined hub of the stator structure. The outer race of each bearing is fitted within the hub. The outer race of a first bearing is bonded within the hub. The second bearing is held in the hub during assembly by a special O-ring member located within an annular recess in the hub. The inner races of the bearings are fitted onto the motor shaft and generally into abutting relation with a locating shoulder on the shaft and an outer hub member on the outer end of the shaft. A steel snap-ring or an integral spacer is interposed within a machined recess in the hub between the two bearings. Suitable flat spring washers are interposed between the snap ring and the respective opposed outer bearings of the two spaced bearings to resilently load the bearings and hold them in position with the desired accuracy and support.
Although the rotary ball bearings have been and presently are in use in commercially available motors, there is a continuing need to improve the operating characteristic of the bearings structure and to minimize the cost.
For example, in the multiple part bearing structure employing the holding O-ring, great care must be taken in the assembly. The inventor has realized that during the assembly of the outer bearing, the O-ring may be trapped between the inner edge of the O-ring recess and the outer race of the bearing. Insertion of the bearing may thus shear a part of the O-ring. Although the removed material may be minute, the material will be located with the bearing chamber within the hub. Any particle within the high precision bearing structure is completely unacceptable because it contributes to a production of bearing noise and may cause deterioration of the bearing. Further, if the material is trapped between the hub and the bearing race, the bearing race having a slight tilt which will also contribute to excessive noise if not bearing disruption. These results thus are unacceptable from a practial and competitive standpoint.
Thus, in such high speed, precision motors, the bearings are often a source of unacceptable noise. Spring loading, precision construction and the O-ring which may dampen noise have been used as necessary to minimize noise. However, the bearings which are commerically available and which the inventor has tested, create a noticable level of noise.
Various other alternative bearing structures can of course be use such as a more conventional sleeve type bearings with very special structures and the like. Such bearing structures however, also have certain disadvantages and difficulties.
There is a need therefore for an improved long-life and low-cost rotary ball bearing support for small permanent magnet motors such as used for disk drives and the like which produce a minimal level of noise.